A low te mperature adiabatic calorimeter and cryostat assembl y is d esc ribed for measUl'ing heat capacit ies in t he te mperature range 10 to 360 oK. A combination of D ewar a nd tank system is used as refrigerant co ntainers. Th e te mperature of t he adia batic shi eld is a utomatically co ntrolled to within a millidegree of t hat of the c" lorimeter vessel. This a ppa rat us offe rs hLCiliti es for rapid cooling to a bout 50 oK and long term a diabatic control for conditionin g of a sa mple and, t hus, is esp ecially sui table for m eas urements on glass, where long eq uilibration t ime is so meti mes involved.D ata on t he empty calorimeter vessel a nd on the Ca,lorimetr y Conference standard sample of sy nt hetic sapp hire a rc presented as a m eas ure of t he precision a nd t he acc uracy of t he a ppa rat us.

The melting point of relatively pure iron was determined at pressures up to 40 kb. When the experimental data are fitted with a straight line of slope 2.85 deg/kb most of the scatter is less than 4°. If observed temperatures are corrected according to Hanneman and Strong for the effect of pressure on thermocouples, the slope of the melting curve becomes 3.8 deg/kb. Some limits upon the melting temperature of iron at higher pressures are obtained by consideration of zero‐pressure and low‐temperature data, as well as high‐pressure data, for iron and its alloys. Because of the considerable ignorance concerning the course of fusion curves at high pressure, it seems unwise to extrapolate the present data in order to estimate temperatures near the center of the earth.

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